Definition
IP warming is the practice of starting with low email volumes from a new sending IP address or domain and gradually increasing over several weeks. The purpose is to establish a positive sending reputation with mailbox providers before ramping up to your full sending volume.
When a new IP address starts sending email, mailbox providers have no historical data on that IP. They treat it with suspicion because spammers frequently rotate through new IPs to avoid detection. By sending low volumes to your most engaged subscribers first and gradually increasing, you demonstrate legitimate sending behaviour and build trust.
Formula
There is no single formula for IP warming, but a common warm-up schedule follows a progressive increase pattern:
Daily Volume = Previous Day Volume × (1 + Growth Rate)
| Variable | Description |
|---|---|
| Previous Day Volume | Number of emails sent the previous day |
| Growth Rate | The rate of daily volume increase (typically 15% - 33%) |
Average Benchmark
| Week | % of Full Volume | Recommended Daily Volume (for 100K/month sender) |
|---|---|---|
| Week 1 | 5% - 10% | 200 - 500 |
| Week 2 | 10% - 20% | 500 - 1,000 |
| Week 3 | 20% - 40% | 1,000 - 2,000 |
| Week 4 | 40% - 60% | 2,000 - 3,000 |
| Week 5 | 60% - 80% | 3,000 - 4,000 |
| Week 6 | 80% - 100% | 4,000 - 5,000 |
A complete warm-up typically takes 4-8 weeks. Longer warm-up periods are recommended for higher volumes or if you are expanding to new geographic regions.
How to Improve IP Warming
- Start with your most engaged subscribers: Send to subscribers who have opened or clicked in the last 30 days. Their positive engagement signals (opens, clicks, replies) build your reputation quickly.
- Monitor engagement metrics daily: Track open rate, click rate, bounce rate, complaint rate, and spam trap hits throughout warm-up. If any metric degrades, hold volume steady until it recovers.
- Maintain consistent sending cadence: Send every day during warm-up, even if volumes are small. Gaps in sending can slow the warm-up process because providers expect consistent patterns.
- Authenticate your domain first: Ensure SPF, DKIM, and DMARC are fully configured before starting warm-up. Sending without authentication from a new IP is a major red flag to mailbox providers.
- Warm up dedicated IPs separately: If you have a dedicated IP, it must be warmed independently. Shared IPs do not require warming because the IP already has a reputation from other senders.
Example Calculation
If you plan to eventually send 100,000 emails per day, and you use a standard 6-week warm-up schedule starting at 500 emails per day with a 25% weekly growth rate:
Week 1: 500/day → total 3,500
Week 2: 625/day → total 4,375
Week 3: 781/day → total 5,467
Week 4: 976/day → total 6,832
Week 5: 1,220/day → total 8,540
Week 6: 1,525/day → total 10,675
After 6 weeks, the IP has a positive reputation built on approximately 39,389 emails sent to engaged subscribers, and you can begin scaling more aggressively toward your 100,000 daily target.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
AMP for Email
AMP for Email is a Google-developed framework that allows email messages to include interactive elements like forms, carousels, accordions, and live content. It turns static emails into dynamic, interactive experiences directly inside the inbox.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Rate
Email bounce rate is the percentage of emails that were rejected by the receiving server before reaching the recipient. It is a key indicator of list health and data quality.
CAN-SPAM Act
The CAN-SPAM Act is a US law that sets rules for commercial email. It requires accurate subject lines, a physical address, a clear opt-out mechanism, and prompt processing of unsubscribes. Violations can result in penalties up to $51,744 per email.
Frequently Asked Questions
IP warming typically takes 4-8 weeks depending on your target sending volume. Lower volumes (under 100,000 per month) can be warmed in 2-4 weeks. Higher volumes (1 million+ per month) may require 8-12 weeks. The warm-up period is shorter if you are sending to highly engaged subscribers and maintaining excellent engagement metrics throughout.
Yes. Domain reputation is now as important as IP reputation, especially with DMARC becoming standard. A new sending domain should be warmed using the same gradual volume approach as a new IP. Many mailbox providers track domain reputation separately and apply the same suspicion to new domains as they do to new IPs.
Sending high volumes from a new IP too quickly is called a "cold send" and is one of the fastest ways to destroy deliverability. Mailbox providers will throttle your sending, route your emails to spam folders, or block your IP entirely. Recovering from a cold send reputation hit takes much longer than warming properly from the start.
Yes. If you are adding a new IP while maintaining your existing sending infrastructure, send only a portion of your engaged subscriber volume through the new IP during warm-up. Keep your main volume on your established IP. Gradually shift traffic to the new IP over the warm-up period as its reputation builds.
No. Shared IPs already have an established reputation from other senders on that IP. The reputation of a shared IP is influenced by all senders using it, not just you. The downside is you have less control — if another sender on your shared IP damages the reputation, it affects your deliverability too.